1. Field of the Invention
The present invention relates to a shear deformation apparatus, and more particularly, to a shear deformation apparatus capable of reducing a deformation resistance and a friction resistance and having a uniform shear deformation, which results in additional effects of reduction in running power and cost.
2. Description of the Conventional Art
As shown in FIG. 1, a shear deformation apparatus generally known as an equal channel angular apparatus comprises: a die 1 in which an inlet channel 2 and an outlet channel having the same sectional area are crossed each other with an ‘L ’ shape; and a pressurizing tool (not shown) for putting a material 3 into the inlet channel 2, then pressurizing and extruding to the outlet channel 4.
When a metallic material is put into an inlet 21 of the shear deformation apparatus and then extruded to an outlet 41, a change in material flow occurs at the intersection of the inlet and outlet channel. This process causes a shear deformation with a shear angle, θ. As the result, the microstructure of the material becomes fine, thereby improving mechanical properties such as strength and formability (Refer to Journal of Metals, 1998, June, Pages 41 to 45).
Under an ideal circumstance having no friction, a shear deformation with θ is generated in the deformed material 5. As there is no change in the cross sectional area of the material during processing, very fine microstructure can be obtained by repeating the process.
However, in the conventional method, the ideal circumstance with no friction can not be obtained even if a lubricant is deposited to an inner wall of the inlet path 2 and the outlet path 4. As a result, as shown in FIG. 2, a non-uniform deformation that the shear angle varies depending on a position is generated, thereby resulting in inhomogeneous structure and properties. Especially, the flow of the material becomes slow at a bottom surface due to a severe friction resistance which causes the material to lag behind to a great degree (Refer to Scripta materiallia, Vol. 37, No. 4, 1997, pages 437 to 442).
Moreover, as shown in FIG. 3, there is a severe deformation resistance and a high frictional resistance at the corner of the die, and a dead zone 6 is generated at this corner where the material is adhered instead of being deformed. This requires an equipment of a high power and a high cost in order to overcome the high resistance of the material flow in the dead zone.
In order to lower a deformation resistance of the dead zone, a method for increasing a die angle Φ was proposed as shown in FIG. 4. In this case, however, since the amount of shear deformation decreases, the microstructure refining effect of the material reduces. Additionally, since the number of repeated processes has to be increased in order to increase the amount of shear deformation, a productivity lowers.
As another method for lowering the deformation resistance and inhomogeneous deformation, the outer edge is made to be round, as shown in FIG. 5, in order to reduce the dead zone. However, in this method, too, the amount of shear deformation of the entire material decreases. In addition, the material near the bottom surface can scarcely have shear deformation, as shown in FIG. 6, even in the ideal state having no friction, thereby causing a problem that the structure and properties of the material become non-uniform. Especially at the bottom surface of the material, deformation becomes very inhomogeneous according to a position since there is little shear deformation owing to a geometric effect of the round edge and frictional lag of the material flow on the contact surface, thereby resulting in a non-uniform material characteristics (Refer to Matallurgical and Materials Transactions 32A, December, 2002, pages 3007 to 3014).